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Title: Investigation of transcriptional and cell cycle regulation in B cell quiescence and activation
Author: Thomsen, Inesa
ISNI:       0000 0004 7655 4843
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 2018
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The quiescent state in mature B cells is actively maintained through a transcriptional programme controlled by multiple transcription factors and cofactors. Failure to appropriately regulate the expression of genes in these cells can have serious pathological consequences. This thesis has sought to investigate the role of various transcriptional and cell cycle regulators in these cells, and their importance during B cell activation. To address these questions, a primary cell model system was employed, where mature resting B cells were freshly isolated from mouse spleens. The study describes a functional interaction between the transcription factor heterodimer RUNX1-CBFB, the mitotic kinase AURKB and the Polycomb protein RING1B. Global chromatin occupancy analysis revealed a significant co-localisation of these proteins on promoters and enhancers in resting B cells. The RUNX1-CBFB heterodimer is shown to be a phosphorylation target of AURKB. The kinase activity of AURKB promotes RUNX1 chromatin binding, whereas RUNX1 appears to play a role in AURKB protein stability in resting B cells. In addition to these findings, AURKB is shown to have an inhibitory interaction with the transcription factor FOXO1 in resting B cells. AURKB phosphorylates FOXO1 on sites overlapping with the AKT phosphorylation sites, hindering FOXO1’s DNA binding capacity. The importance of RUNX1 in resting B-cells is highlighted in this study by using a conditional mouse knockout system, in which Runx1 is deleted at the transitional B-cell developmental stage. These Runx1 knockout mice have reduced numbers of splenic resting B-cells and lymph node B-cells. Ex vivo, Runx1 knockout resting B-cells exhibit a hyper-responsive phenotype to mitogenic stimulation. Analyses of the splenic B-cell subsets suggest a possible role for RUNX1 in follicular type I B-cell development or survival. Finally, the evidence presented in this thesis suggests a potential role for RUNX1 in suppressing the development of autoimmunity.
Supervisor: Dillon, Niall Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral